MK-677

MK-677, also called ibutamoren, is a non-peptide small-molecule research chemical, not a peptide. Its free-base molecular formula is C27H36N4O5S with a molecular weight of 528.7 g/mol, and it is commonly isolated as the mesylate salt at C28H40N4O8S2 and 624.8 g/mol. The scaffold is a spiroindoline linked to a piperidine, with a methanesulfonyl group and a benzyl ether side chain, a structure assembled by conventional medicinal chemistry rather than by peptide synthesis. It carries the internal designations MK-0677 and L-163,191 from its development programme, and it is supplied here in a solid unit-dose format as a research-use-only reference compound.

The published literature describes MK-677 as a peptidomimetic, a small molecule designed to reproduce the receptor interaction of a peptide without being one. Its target is the growth hormone secretagogue receptor GHS-R1a, the same receptor engaged by ghrelin and by the GHRP-family peptides. MK-677 holds no regulatory approval in any jurisdiction, and its development programme did not result in an approved product. Within the growth hormone secretagogue literature it functions as the standard non-peptide reference agonist for that receptor, and it is frequently and incorrectly filed alongside research peptides in catalogues and reference lists.

MK-677 came out of a Merck programme that started from the GHRP peptides and worked through non-peptide intermediates, including the benzolactam series, toward a small-molecule scaffold. Patchett and colleagues reported the design and biological activity of L-163,191, later MK-0677, in 1995 (PubMed 7624358).

Receptor-level context arrived alongside it. Howard and colleagues cloned the growth hormone secretagogue receptor and characterised it as the target of this compound class (PubMed 8688086). Smith and colleagues reviewed peptidomimetic secretagogue pharmacology (PubMed 9331545), and Kojima and colleagues identified ghrelin as the receptor’s endogenous ligand (PubMed 10604470).

The evidence base is well developed at the receptor and preclinical level and closed as a development programme. Binding, selectivity and animal pharmacology are documented. No approval followed, and no efficacy conclusion should be drawn here.

Published work describes MK-677 as an agonist at GHS-R1a, a Gq/11-coupled receptor. The reported cascade runs through phospholipase C, inositol trisphosphate and diacylglycerol generation and intracellular calcium mobilisation in pituitary cell preparations. These are receptor-level and cell-level descriptions, not statements about an outcome in an intact organism.

Two distinctions are useful. MK-677 shares a receptor with GHRP-6, hexarelin and ipamorelin but not a chemical class, while sermorelin, tesamorelin, CJC-1295 and Mod GRF 1-29 act at the separate GHRH receptor. Separately, MK-677 is routinely confused with selective androgen receptor modulators carrying similar MK codes, and it has no reported androgen receptor activity.

A methodology caveat applies. Much of the record comes from receptor binding assays, pituitary cell systems and animal models in which secretagogue receptor pharmacology differs by species, so reported potencies belong to the assay used.

Sealed MK-677 reference material is stored cool, dry and shielded from light, with freezer storage at -20°C conventional for long-term holding of small-molecule standards. No duration is stated here: the stability window is documented on the batch Certificate of Analysis.

Small molecules of this type are generally less thermolabile than peptides, but the mesylate salt is hygroscopic, meaning it takes up atmospheric moisture, which affects weighed accuracy. Capsules are stored under the conditions given on the product label.

Reconstitution is the term for returning a solid compound to solution; this page defines the term and gives no procedure. MK-677 sits in the small-molecule solubility class, with limited aqueous solubility as the free base and DMSO the general in vitro solvent class for compounds of this type.

Solid material is best handled in low humidity with minimal open-container exposure. Preparation parameters belong to the published methodology being reproduced, read alongside the Certificate of Analysis for the lot in hand.

Identity and purity for a small molecule are established by HPLC with ultraviolet detection, liquid chromatography with mass spectrometry, and where required nuclear magnetic resonance. The primary identity check is a mass consistent with 528.7 g/mol for the free base, or 624.8 g/mol for the mesylate salt. Verified purity is documented per lot on the Certificate of Analysis.

Salt form matters when reconciling a stated strength, because free base and mesylate differ by roughly 96 g/mol. For a solid unit-dose format, identity of the fill and content uniformity are the relevant specifications. Catalyst Compounds material is batch tested with a published Certificate of Analysis.

MK-677 is the non-peptide member of a group otherwise made up of peptides.

• GHRP-6.
  A synthetic hexapeptide at the same ghrelin receptor, the peptide starting point for the chemistry that produced MK-677.
• Hexarelin and Ipamorelin.
  Further ghrelin receptor peptides, used as class comparators in receptor pharmacology.
• Sermorelin, CJC-1295 and Tesamorelin.
  GHRH-receptor analogues acting at a different receptor, not ghrelin receptor ligands.
• Mod GRF 1-29.
  A further GHRH-receptor analogue, useful as a receptor-specificity control.
• IGF-1 LR3.
  A growth factor receptor ligand rather than a secretagogue, a third mechanism again.

Patchett AA, Nargund RP, et al. (1995). Design and biological activities of L-163,191 (MK-0677): a potent, orally active growth hormone secretagogue. Proc Natl Acad Sci U S A.
PubMed 7624358

Howard AD, Feighner SD, et al. (1996). A receptor in pituitary and hypothalamus that functions in growth hormone release. Science.
PubMed 8688086

Smith RG, Van der Ploeg LH, et al. (1997). Peptidomimetic regulation of growth hormone secretion. Endocr Rev.
PubMed 9331545

Kojima M, Hosoda H, et al. (1999). Ghrelin is a growth-hormone-releasing acylated peptide from stomach. Nature.
PubMed 10604470

MK-677 is stocked in a single solid unit-dose format, capsules, from one house brand at a listed 12.5mg strength. There is no vial or liquid spray listing for this compound at present. The strength shown is a product specification, and each lot is batch tested with a published Certificate of Analysis.

• Browse all MK-677 research products
• Catalyst Compounds MK-677 Capsules, 12.5mg
• Collections: Capsules & Tablets. Documentation: COA and Lab Testing.

These products are sold for Research Use Only and are not intended for human consumption.